1. Field of the Invention
This invention relates to heavy duty vehicles or the like for on or off road travel as may be classed as rough terrain vehicles and more particularly to such a vehicle having an articulate box frame incorporating three point suspension and rear wheel progressive steering.
2. Brief Description of the Prior Art
In the past, it has been the conventional practice in the design and construction of heavy duty vehicles such as trucks, cargo carriers, busses, ambulances, cars and the like to provide a rigid frame or chassis having the carrying ability to transport heavy loads over highways and unimproved roads and somewhat rough terrain. Most of these prior vehicles are not capable of operating satisfactorily in rough terrain due to the fact that no means are provided for off-setting the high torque loads applied to the chassis, equalizing the load to the chassis or for maintaining the support wheels of the various axles equally loaded in contact with the terrain over which the vehicle passes. Furthermore, no mechanism is provided for compensating or load leveling the chassis while the vehicle is traveling on angled banks, crowned highways or roadways. In such prior designs, it is common practice to employ walking beams to support the axles in order to maintain adequate surface engagement or contact between the support wheels and the terrain over which the vehicle passes. When wheels are attached directly to the walking beams, problems are encountered when braking is initiated. For example, the resistance of the front walking beam wheel tends to tuck under which causes the rear wheel to rise from surface contact and be less effective in braking. The opposite effect is encountered in acceleration with a tendency to raise the forward wheel from surface contact.
While the development of prior heavy-duty multiple axle vehicles has been the subject of a substantial amount of design and research, it has been found that costly vehicle repairs result from the high torsional loads applied to the vehicle chassis. Therefore, in most cases where roads do not exist, dirt and sometimes asphalt roads are provided.
Still another problem with conventional heavy-duty vehicles resides in the scuffing of wheels when the vehicle is rounding a curve such as in the case of a vehicle having more than two axles.
Therefore, a long standing need has existed to provide a vehicle chassis capable of operating in rough terrain having a construction for compensating applied torsional loads, for equalizing the load while traveling on angled or crowned roadways and for maintaining wheel surface contact under a variety of vehicle operating conditions.